Half a croissant, on a plate, with a sign in front of it saying '50c'
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Passenger jet with hot air balloon

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(+2, -4)
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Divert hot air from the jet exhaust to a big hot air balloon floating high above the aeroplane. Then the jets only have to provide forward thrust, not lift.
hippo, Feb 17 2009


       How big? Did you do any sums?
wagster, Feb 17 2009

       sums? - er, ... no
hippo, Feb 17 2009

       140.000kg Jetliner, 3 cubic_metres of air at 120° to lift a kg -> 420.000 cubic metres of very hot air,heated by jet turbines that are trying to drag it along...   

       Congrats,your idea just topped the size of the biggest airship ever, which had only 200.000m3
loonquawl, Feb 17 2009

       Also, the plane would have to carry extra fuel to overcome the drag from the balloon.
MaxwellBuchanan, Feb 17 2009

       The Hullaballoon lends itself to fast, aerodynamic flight, but I think not in the range normally used by a jet engine.
FlyingToaster, Feb 19 2009

       Also, if you divert hot air from the jet exhaust to a balloon, you rob it of thrust. Also, jet engines are highly inefficient for low speed flight.   

       Perhaps generalised to 'use the waste heat from the engines to provide the hot air in a hot air dirigible' there might be more scope for this to work.   

       A hullaballoon, averaged by volume, might actually move backwards. Kind of.
spidermother, Feb 21 2009

       Well, ya can't say it's not half baked.   

       This is the 'Crazy Eddie'est idea I've seen in my short time on this site. In addition, it comes swiftly to the point, which I like. Further, it's pointless, which I'm coming to enjoy.   

       However, even pointlessness must have a limit, and here, that limit been exceeded -- nay, trashed...maybe even smithereened.   

       Kudos, hippo. Enjoy your fish.
colorclocks, Feb 21 2009

       [sm] a hullaballoon isn't going to move backwards, the lifting medium (H2 or He) has to be transferred from the collapsing balloonettes to the expanding ones... movement-wise it's totally an air tractor.
FlyingToaster, Feb 21 2009


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